1. Field of the Invention
The present invention relates to a clutch control system for a transmission. More particularly, to a clutch control system for a transmission which can appropriately perform preparations for driving a plurality of hydraulic clutches driven by oil pressures supplied from a hydraulic pump, at an engine starting time.
2. Description of Background Art
Hitherto, there has been known a transmission which has a hydraulic pump driven attendantly on the rotation of a crankshaft and in which connection/disconnection of a clutch is controlled by an oil pressure generated by the hydraulic pump. In such a hydraulic type clutch, when the supply of the oil pressure is stopped attendantly on stopping of the engine, a working oil filling up an oil passage for the purpose of transmitting the oil pressure may be lost little by little from the oil passage due to leakage through gaps present in lubricated parts, leakage from hydraulic devices, or the like. At the time of first driving the clutch by starting the engine under the condition where the working oil has been partly lost from the oil passage, even if the oil pressure is supplied from the hydraulic pump according to a clutch driving command, it would take a little time for the oil passage to be again filled up with the working oil. As a result, at the time of first driving the clutch after the starting of the engine, an operational delay may be generated in relation to the driving command.
Japanese Patent Laid-Open No. 2001-141045 discloses a clutch control system for a transmission having a plurality of clutches corresponding to a plurality of gear speeds, wherein at an engine starting time, an oil pressure generated by a hydraulic pump is automatically supplied into oil passages, whereby the oil passages are filled up with the working oil before a clutch driving command is issued, and a delay in clutch operation is prevented from being generated.
In the technology according to Japanese Patent Laid-Open No. 2001-141045, however, in order to fill up the oil passages connected to the plurality of clutches with the working oil, the respective times to supply the oil pressures into the oil passages are computed from pipeline volume, engine speed and oil temperature, so that a complicated control is needed.
In addition, where the above-mentioned computation of the times to supply the oil pressures is not conducted and the oil pressures are supplied into the plurality of oil passages at the same time, the following problem may be generated. FIGS. 5(a) and 5(b) show graphs illustrating an example of the preparations for the driving of clutches in a twin-clutch type transmission having two hydraulic clutches CL1 and CL2. The clutches CL1 and CL2 are so configured that they show strokes in the directions for connection, attendantly on the supply of the oil pressures, and a predetermined oil pressure Pc is set at such a value that CL1 and CL2 show sufficient strokes, to be switched into a connected state. In this example, as preparations for driving of the clutches, the oil passages from which the working oil has been partly lost are again filled up with the working oil, and, for this purpose, it is aimed at generating the predetermined oil pressure Pc at each of CL1 and CL2. In addition, a master oil pressure Pm supplied from a hydraulic pump is set so as to have a little allowance (margin) in relation to the predetermined oil pressure Pc.
In this case, if the supplies of oil pressures to CL1 and CL2 are simultaneously started so as to realize the target oil pressure shown in FIG. 5(a), a working oil quantity, in excess of a supply quantity such that the hydraulic pump can maintain the master oil pressure Pm, is needed instantaneously. This results in that the master oil pressure Pm is lowered, and, as shown in FIG. 5(b), actual oil pressures generated at CL1 and CL2 do not conform to the target oil pressure, and the preparations for driving of the clutches are not carried out smoothly. In addition, although the lowering of the master oil pressure Pm can be prevented if the capacity of the hydraulic pump is increased sufficiently, it is undesirable to enlarge the hydraulic pump in order to secure the capacity that is needed only for the preparations for driving of the clutches.